P–PINI: A cosmogenic nuclide burial dating method for landscapes undergoing non-steady erosion

Existing methods of cosmogenic nuclide burial dating perform well provided that sediment sources undergo steady rates of erosion and the samples experience continuous exposure to cosmic rays. These premises exert important limitations on the applicability of the methods. And yet, high mountain sediment sources are rife with transient processes, such as non-steady erosion by glacial quarrying and/or landsliding, or temporary cosmic-ray shielding beneath glaciers and/or sediment. As well as breaching the premises of existing burial dating methods, such processes yield samples with low nuclide abundances and variable ²⁶Al/¹⁰Be ratios that may foil both isochron and simple burial-age solutions. P–PINI (Particle-Pathway Inversion of Nuclide Inventories) is a new dating tool designed for dating the burial of sediments sourced from landscapes characterized by abrupt, non-steady erosion, discontinuous exposure, and catchments with elevation-dependent ²⁶Al/¹⁰Be production ratios. P–PINI merges a Monte Carlo simulator with established cosmogenic nuclide production equations to simulate millions of samples (¹⁰Be–²⁶Al inventories). The simulated samples are compared statistically with ¹⁰Be–²⁶Al measured in field samples to define the most probable burial age. Here, we target three published ¹⁰Be–²⁶Al datasets to demonstrate the versatility of the P–PINI model for dating fluvial and glacial sediments. (1) The first case serves as a robust validation of P–PINI. For the Pulu fluvial gravels (China), we obtain a burial age of 1.27 ± 0.10 Ma (1σ), which accords with the isochron burial age and two independent chronometers reported in Zhao et al. (2016) Quaternary Geochronology 34, 75–80. The second and third cases, however, reveal marked divergence between P–PINI and isochron-derived ages. (2) For the fluvial Nenana Gravel (USA), we obtain a minimum-limiting burial age of 4.5 ± 0.7 Ma (1σ), which is compatible with unroofing of the Alaska Range starting ∼ 6 Ma, while calling into question the Early Pleistocene isochron burial age presented in Sortor et al. (2021) Geology 49, 1473–1477. (3) For the Bünten Till (Switzerland), we obtain a limiting burial age of <204 ka (95th percentile range), which conforms with the classical notion of the most extensive glaciation in the northern Alpine Foreland assigned to the Riss glaciation (sensu marine isotope stage 6) contrary to the isochron burial age presented in Dieleman et al. (2022) Geosciences, 12, 39. Discrepancies between P–PINI and the isochron ages are rooted in the challenges posed by the diverse pre-burial ²⁶Al/¹⁰Be ratios produced under conditions characteristic of high mountain landscapes; i.e., non-steady erosion, discontinuous cosmic-ray exposure, and elevation-dependent ²⁶Al/¹⁰Be production ratios in the source region, which are incompatible with the isochron method, but easily accommodated by the stochastic design of P–PINI.     

Complex exposure histories of chert clasts in the late Pleistocene shorelines of Lake Lisan,southern Israel

Activities of ²⁶Al and ¹⁰Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert‐bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio ²⁶Al/¹⁰Be, total clast histories range from 0·46 to 4·3 My, unrelated to the clasts' current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20·0 ± 1·4 ka and 36·1 ± 3·3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP . If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0·4 and 12 m My^?1. The relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright © 2003 John Wiley & Sons, Ltd.     

Radiometric dating of Meipu hominin site in China by coupled ESR/U-series and cosmogenic 26Al/10Be burial dating methods

The Three Gorges and Western Hubei area in the geographic central part of China was a potential migration corridor for early hominin and mammals linking South and North China during the Pleistocene period. Some key early hominin sites are known in this region where limestone cave and fissure sites are numerous but difficult to date as beyond the dating range of OSL and mass spectrometry U-series method. Here, we report radiometric dating study for such a hominin site, Meipu (Hubei Province), by coupled ESR and U-series dating of nine fossil teeth and cosmogenic ²⁶Al/¹⁰Be burial dating of one quartz sediment. The burial age calculated by simple burial model (573 ± 266 ka) gives a minimum age constraint of the sediment. The fossil dating provided two main age groups at 541 ± 48 ka and 849 ± 39 ka, the older age group is in agreement with the U-series age (>630 ka) of the flowstone overlying the fossil layer and the paleomagnetic data which placed the Brunhes-Matuyama boundary in the fossil layer. The reason of this age difference is probably caused by the U-content discrepancy in the enamel of the dated fossil samples. This study exhibits the limitation of ESR/U-series fossil dating and the importance of using multiple dating approach when it is possible in order to identify the problematic ages.     

Fuerteventura – Assessment of a calibration site for cosmogenic 3He exposure dating with the 40Ar/39Ar incremental heating method

In situ Terrestrial Cosmogenic Nuclides (hereafter TCNs) are increasingly important for absolutely dating terrestrial events and processes. This study aimed at improving our knowledge of the production rate of Terrestrial Cosmogenic ³He formed in situ in rock surfaces at low latitude and sea level as well as re-evaluation of the Canary Islands as a calibration site for TCNs. For this purpose, we sampled basaltic lava flows from some of the youngest and yet undated volcanic sites and used the ⁴⁰Ar/³⁹Ar incremental heating method on groundmass samples and in situ cosmogenic ³He on olivine and clinopyroxene phenocrysts. ⁴⁰Ar/³⁹Ar analysis was done on a Hiden HAL Series 1000 triple filter quadrupole mass spectrometer with extraction furnace. Incremental heating data shows ages in the Late Pleistocene from 52.7 ± 21.6 ka to 398.6 ± 27.6 ka.We measured cosmogenic ³He concentrations in olivine and clinopyroxene phenocrysts from flow top samples on a MAP 215-50 sector mass spectrometer with a crushing device and a diode laser extraction system. Exposure age calculations yielded ages in the range 38.9 ± 4.0 ka to 62.3 ± 6.7 ka for the youngest lava flow and the data series is in broad agreement with the argon data up to 250 ka and reveals a more continuous time line of volcanism during the late Pleistocene on the island. However, the dataset was not sufficient for calculation of production rates for in situ Terrestrial Cosmogenic ³He as many samples showed signs of erosion. Calculated erosion rates range from none to as high as 7.3 mm/kyr assuming a rock density of 2.9 g/cm². This finding puts a constraint on the use of Fuerteventura as a calibration site for exposure histories older than 50–100 ka. A comparison with cosmogenic ³⁶Cl data supports these findings and indicates substantial weathering.     

40Ar/39Ar and ESR/U-series dates for Guado San Nicola,Middle Pleistocene key site at the Lower/Middle Palaeolithic transition in Italy

The Middle Pleistocene archaeological site of Guado San Nicola was discovered in 2005 in a fossil fluvial terrace of the Volturno River, close to the village of Monteroduni, Molise, Italy. Palaeontological remains and lithic artefacts, including both handaxes and Levallois, discoid and opportunistic debitage, were recovered in fluvial and slope sediments rich in volcanoclastic materials. This site includes four distinct human occupation levels. In two of them both “shaping-façonnage” and “knapping-débitage” technologies are highlighted, placing this site at the Lower/Middle Palaeolithic transition.In the present study, geochronological analyses by ⁴⁰Ar/³⁹Ar on single-crystal and ESR/U-series on teeth were performed to precise the chronological framework of the occupations. The ⁴⁰Ar/³⁹Ar data obtained securely bracket the human occupation levels at the transition between the interglacial and glacial marine isotopic stages MIS 11 (i.e. 400 ± 9 ka) and MIS 10 (i.e. 345 ± 9ka). The weighted mean age obtained from ESR/U-series dating of six teeth (i.e. 364 ± 36 ka) is in very good agreement with the ⁴⁰Ar/³⁹Ar results. The radio-isotopic constraints we presented place the Guado San Nicola site as one of the earliest testimonies of Levallois debitage in Western Europe and confirm the potential and accuracy of paleo-dosimetric methods to date Middle Pleistocene sites.     

Evaluating Quaternary dating methods: Radiocarbon,U-series,luminescence, and amino acid racemization dates of a late Pleistocene emu egg

A whole emu egg, with infilling sediment believed to be coeval with egg laying and burial, was found in late Pleistocene lunette sediments near Lake Eyre, central Australia. The stratigraphic context and initial amino acid racemization (AAR) results suggested an age between 25 ka and 35 ka, ideal for a multiple cross-dating comparison. The sediment infilling the egg provided material for luminescence dating that minimized problems of association. Age estimations from AAR, ¹⁴C and U series methods were obtained from the eggshell and optically stimulated luminescence (OSL) of the infilling sediment. All methods agreed within their respective dating uncertainties confirming the utility of all four methods. They indicate an age for the emu egg of 31.24 ± 0.34 ka.     

High-precision 40Ar/39Ar dating of pleistocene tuffs and temporal anchoring of the Matuyama-Brunhes boundary

High-precision ⁴⁰Ar/³⁹Ar ages for a series of proximal tuffs from the Toba super-volcano in Indonesia, and the Bishop Tuff and Lava Creek Tuff B in North America have been obtained. Core from Ocean Drilling Project Site 758 in the eastern equatorial Indian Ocean contains discrete tephra layers that we have geochemically correlated to the Young Toba Tuff (73.7 ± 0.3 ka), Middle Toba Tuff (502 ± 0.7 ka) and two eruptions (OTTA and OTTB) related to the Old Toba Tuff (792.4 ± 0.5 and 785.6 ± 0.7 ka, respectively) (⁴⁰Ar/³⁹Ar data reported as full external precision, 1 sigma). Within ODP 758 Termination IX is coincident with OTTB and hence this age tightly constrains the transition from Marine Isotope Stage 19–20 for the Indian Ocean. The core also preserves the location of the Australasian tektites, and the Matuyama-Brunhes boundary with Bayesian age-depth models used to determine the ages of these events, c. 786 and c. 784 ka, respectively. In North America, the Bishop Tuff (766.6 ± 0.4 ka) and Lava Creek Tuff B (627.0 ± 1.5 ka) have quantifiable stratigraphic relationships to the Matuyama-Brunhes boundary. Linear age-depth extrapolation, allowing for uncertainties associated with potential hiatuses in five different terrestrial sections, defines a geomagnetic reversal age of 789 ± 6 ka. Considering our data with respect to the previously published age data for the Matuyama-Brunhes boundary of Sagnotti et al. (2014), we suggest at the level of temporal resolution currently attainable using radioisotopic dating the last reversal of Earths geomagnetic field was isochronous. An overall Matuyama-Brunhes reversal age of 783.4 ± 0.6 ka is calculated, which allowing for inherent uncertainties in the astronomical dating approach, is indistinguishable from the LR04 stack age (780 ± 5 ka) for the geomagnetic boundary. Our high-precision age is 10 ± 2 ka older than the Matuyama-Brunhes boundary age of 773 ± 1 ka, as reported previously by Channell et al. (2010) for Atlantic Ocean records. As ODP 758 features in the LR04 marine stack, the high-precision ⁴⁰Ar/³⁹Ar ages determined here, as well as the Matuyama-Brunhes boundary age, can be used as temporally accurate and precise anchors for the Pleistocene time scale.     

Isochron‐burial dating of glaciofluvial deposits: First results from the Swiss Alps

In this study, we use isochron‐burial dating to date the Swiss Deckenschotter, the oldest Quaternary deposits of the northern Alpine Foreland. Concentrations of cosmogenic ¹⁰Be and ²⁶Al in individual clasts from a single stratigraphic horizon can be used to calculate an isochron‐burial age based on an assumed initial ratio and the measured ²⁶Al/¹⁰Be ratio. We suggest that, owing to deep and repeated glacial erosion, the initial isochron ratio of glacial landscapes at the time of burial varies between 6.75 and 8.4. Analysis of 22 clasts of different lithology, shape, and size from one 0.5 m thick gravel bed at Siglistorf (Canton Aargau) indicates low nuclide concentrations: <20 000 ¹⁰Be atoms/g and <150 000 ²⁶Al atoms/g. Using an ²⁶Al/¹⁰Be ratio of 7.6 (arithmetical mean of 6.75 and 8.4), we calculate a mean isochron‐burial age of 1.5 ± 0.2 Ma. This age points to an average bedrock incision rate between 0.13 and 0.17 mm/a. Age data from the Irchel, Stadlerberg, and Siglistorf sites show that the Higher Swiss Deckenschotter was deposited between 2.5 and 1.3 Ma. Our results indicate that isochron‐burial dating can be successfully applied to glaciofluvial sediments despite very low cosmogenic nuclide concentrations. Copyright © 2017 John Wiley & Sons, Ltd.     

MET-post-IR IRSL luminescence dating of cobbles buried in fluvial terraces in the Northern Chinese Tian Shan

Cobbles can be used as an alternative to the conventionally employed sand-sized mineral luminescence dating. In piedmont environments, cobbles are much more abundant than sand-sized material. The IRSL₅₀ signal has been widely used in previous studies due to its greater sensitivity to exposure events. However, it is well known that the low temperature IRSL signal is more prone to fade than elevated temperature post-IR IRSL signal. In this study, to test the reliability and applicability of cobble sub-surface elevated temperature IRSL luminescence dating, six light-color granite cobbles and two sand-sized samples from silty sand lens were collected from a high terrace of Manas River on the northern piedmont of Chinese Tian Shan. A modified multi-elevated-temperature post-infrared infrared stimulated luminescence (MET-post-IR IRSL) protocol was applied. The age-temperature (A-T) plateau of MET-post-IR IRSL measurement was combined with the conventional age-depth (A-D) plateau in luminescence-depth profile to evaluate the resetting and fading of MET-post-IR IRSL signals. Uncertainties of grain-sizes of K-feldspar within solidified slices were also explored by μ-XRF mapping of potassium content. The A-T plateau was identified between MET-post-IR IRSL₁₇₀ and MET-post-IR IRSL₂₂₅ signals of one cobble, which suggested completeness of bleaching before burial and negligible anomalous fading during burial. This cobble yielded MET-post-IR IRSL₂₂₅ ages of 15.8 ± 2.6 ka and 19.0 ± 3.2 ka for top and bottom side, respectively. These MET-post-IR IRSL₂₂₅ ages were consistent with independent coarse-grained quartz MAM OSL ages (15.7 ± 3.6 ka and 14.8 ± 2.6 ka) of two sand-sized samples. The MET-post-IR IRSL₂₂₅ age of 16.0 ± 1.2 ka for the bottom side of another cobble was also consistent with the independent age, even without the A-T plateau. It was inferred to be caused by anomalous fading of MET-post-IR IRSL signals other than that stimulated at 225 °C by refering to the A-D plateau observed. Our results show that MET-post-IR IRSL measurement can be employed to determine the burial ages of cobbles. The A-T plateau, complemented with the A-D plateau, could be used to assess the reliability of burial ages of cobble luminescence dating from the view of bleaching and fading.     

Non-steady long-term uplift rates and Pleistocene marine terrace development along the Andean margin of Chile (31°S) inferred from 10Be dating

Pleistocene uplift of the Chilean coast is recorded by the formation of wave-cut platforms resulting from marine erosion during sea-level highstands. In the Altos de Talinay area (~ 31°S), we have identified a sequence of 5 wave-cut platforms. Using in situ produced ¹⁰Be exposure ages we show that these platforms were formed during interglacial periods at 6, 122, 232, 321 and 690 ka. These ages correspond to marine isotopic stages (MIS) or substages (MISS) 1, 5e, 7e, 9c and 17. Shoreline angle elevations used in conjunction with our chronology of wave-cut platform formation, illustrate that surface uplift rates vary from 103 ± 69 mm/ka between 122 and 6 ka, to 1158 ± 416 mm/ka between 321 and 232 ka. The absence of preserved platforms related to the MIS 11, 13 and 15 highstands likely reflects slow uplift rates during these times. We suggest that since 700 ka, the Altos de Talinay area was predominantly uplifted during 2 short periods following MIS 17 and MISS 9c. This episodic uplift of the Chilean coast in the Pleistocene may result from subduction related processes, such as pulses of tectonic accretion at the base of the forearc wedge.     

Dating of megaflood deposits in the Russian Altai using rock surface luminescence

Catastrophic drainage of ice-dammed lakes in the Altai Mountains has been inferred from geomorphological evidence in the Katun Valley (Russia), and is presumed to have occurred during the Pleistocene. The sedimentary features have been difficult to date directly, due to the absence of organic carbon, and the improbability that luminescence signals in sand grains would be reset during transport. However, the development of rock-surface luminescence dating provides a new opportunity to date the features: clasts have a different transport history to sand grains, and their luminescence depth profiles can be inspected for evidence of bleaching before burial. Here we investigate two sites in the Altai Mountains, and use rock-surface luminescence burial dating to constrain the age of the megaflood deposits. In the Katun Valley, we sampled granite cobbles from a frozen sediment clast emplaced as a dropstone within a massive megaflood gravel terrace. Burial ages for the clasts range from 16.7 to 21.4 ka, with a mean age of 19.8 ± 1.5 ka. This represents the depositional age of the fluvial sediments that preceded the lake outburst flood, (and hence places a maximum age on the catastrophic flood). Clasts sampled from mega-ripples in the Kurai Basin are shown to have a mid-to-late Holocene burial age, which is not consistent with the possible origin of these features during a catastrophic drainage of a glacier-dammed lake. Instead, the burial age of the Kurai Basin sediments may reflect local-scale periglacial or seismic processes along the Kurai Fault Zone.     

Coupled ESR and U-series dating of early Pleistocene Gigantopithecus faunas at Mohui and Sanhe Caves,Guangxi, southern China

Several caves of the Guangxi Zhuang Autonomous Region, southern China, have delivered Gigantopithecus blacki remains, an extinct Pleistocene giant ape, in association with abundant mammalian faunas. To determine their geological ages, fossil teeth from Mohui and Sanhe Caves were dated using the coupled ESR/U-series method. The teeth from Mohui Cave gave age estimates of 1.69 ± 0.22 Ma and 1.29 ± 0.11 Ma. The Sanhe Cave samples had age estimates ranging from 910 ± 200 ka to 600 ± 150 ka with error weighted mean ages of 890 ± 130 ka and 720 ± 90 ka for the layers 5 and 4, respectively. Our results and previous paleomagnestism data place the Gigantopithecus fauna at Mohui Cave between Olduvai and Jaramillo subchrons and suggest that it was coeval with Chuifeng, Longgupo and Liucheng assemblages. The Sanhe fauna is younger, of late early Pleistocene age, and can be dated to the period between Jaramillo subchron and B/M boundary.     

Refining the Quaternary Geomagnetic Instability Time Scale (GITS): Lava flow recordings of the Blake and Post-Blake excursions

The Blake excursion was among the first recognized with directional and intensity behavior known mainly from marine sediment and Chinese loess. Age estimates for the directional shifts in sediments are poorly constrained to about 118−100 ka, i.e., at the marine isotope stage (MIS) 5e/5d boundary. Moreover, sediments at Lac du Bouchet maar, France and along the Portuguese margin reveal what may be a "post-Blake" excursion at about 105−95 ka. The excursional directions are associated with a prominent paleointensity minimum between about 125 and 95 ka in global stacked records. Lava flow recordings of the Blake excursion(s) have, however, been questionable because precise ages required for correlation with these sediment records are lacking. To establish new, independent records of the Blake excursion, and link these into a larger Quaternary GITS, we have undertaken ⁴⁰Ar/³⁹Ar incremental heating and unspiked K-Ar experiments on groundmass from the transitionally magnetized Inzolfato flow on Lipari Island. We also obtained ⁴⁰Ar/³⁹Ar incremental heating results for a lava flow on Amsterdam Island originally thought to record the Mono Lake excursion and from the transitionally magnetized El Calderon basalt flow, New Mexico that was K-Ar dated by Champion et al. (1988) at 128 ± 66 ka.Unspiked K-Ar ages of four samples from the Inzolfato flow are 102.5 ± 4.7, 101.3 ± 3.3, 97.1 ± 2.6, and 96.8 ± 3.1 ka and thus indistinguishable from one another. ⁴⁰Ar/³⁹Ar results are more complex, with three samples yielding discordant age spectra. Based on incremental heating data obtained in both the UW-Madison and Gif-sur-Yvette ⁴⁰Ar/³⁹Ar laboratories, a fourth sample yields six concordant age plateaus and a weighted mean age of 105.2 ± 1.4 ka that we take as the best estimate of time since the flow erupted. Five ⁴⁰Ar/³⁹Ar incremental heating experiments on the Amsterdam Island lava yield a plateau age of 120 ± 12 ka, whereas ages from two sites in the Calderon flow are 112 ± 23 and 101 ± 14 ka, together giving a weighted mean of 104 ± 12 ka. The age of 120 ± 12 ka from Amsterdam Island, though imprecise, correlates with the Blake excursion. In contrast, the 104–105 ka age obtained from both Lipari and New Mexico indicates that these lavas record a younger period of dynamo instability, most probably associated with the post-Blake excursion. These radioisotopic ages are consistent with the astronomical ages of two paleointensity minima in the PISO-1500 global stack. Our findings indicate that the Blake and post-Blake excursions are both global features of past geodynamo behavior and support the hypothesis that Brunhes chron excursions are temporally clustered into two groups of at least a half-dozen each spanning over 220 to 30 ka and 720 to 520 ka.     

Age comparison by luminescence using quartz and feldspar on core HPQK01 from the Pearl River delta in China

Reliable chronology is critical for reconstructing estuarine delta process. In this study, detailed chronological framework has been performed on a core HPQK01 (52 m in depth) from the central Pearl River delta (PRD) of China. Both quartz OSL and feldspar post-IR IRSL (pIRIR) methods for late Pleistocene sediments, as well as radiocarbon dating for Holocene sediments, were applied to date the core. Results show that quartz OSL ages range from 125 ± 18 ka to 58 ± 6 ka, and that all of them were minimum ages due to the OSL signal saturation. Feldspar pIR₂₀₀IR₂₉₀ protocol shows some overestimation in dose recovery test, with the recovered to the given ratio of 1.2, while a ratio of around 1 was obtained for feldspar pIR₅₀IR₂₅₀ signals. Robust ages have been obtained from feldspar fading corrected pIR₅₀IR₂₅₀ dating with ages ranging from 150 ± 17 ka to 98 ± 12 ka. AMS ¹⁴C results suggest that subtidal-intertidal zone was deposited during the middle Holocene from 8.21 ± 0.19 cal ka BP to 4.99 ± 0.25 cal ka BP. The sedimentology of core HPQK01 record two marine transgressive-regressive cycles. Based on the dating results, the lower fluvial sediment unit (T2) could be correlated to marine isotope stage (MIS) 6, and the lower marine unit (M2) was deposited during MIS 5. A sedimentary hiatus occurred with age range of from MIS 4 to MIS 2. Since middle Holocene, another marine stratum (M1) has been accumulated. Overall, our findings suggest that feldspar pIRIR dating method has the potential to establish the Quaternary chronostratigraphic framework of the PRD for samples with ages within 150 ka.     

Meteoric 10Be concentrations from saprolite and till in northern Sweden: Implications for glacial erosion and age

We examine ¹⁰Be concentration in two pit profiles in the Parkajoki area at ∼67°N on the northern Fennoscandian shield in northern Sweden. Due to repeated cover by cold-based, non-erosive ice sheets, the area retains many relict non-glacial features, including tors and saprolites. In the examined pit profiles, gruss-type saprolite developed from weathering of intermediate igneous rocks is overlain unconformably by Weichselian till.Our results show that ¹⁰Be concentrations found in the till greatly exceed the levels of ¹⁰Be that can have accumulated since deglaciation at ∼11 ka and are comparable to those reported from Pliocene and Early Pleistocene tills in North America. Old tills with grussified boulders at depth were excavated in the Parkajoki area and correlations with neighbouring parts of Finland indicate a Middle Pleistocene or older age. Evidence from pit excavations and geochemistry shows that the underlying saprolites have been truncated by glacial erosion and that previously weathered material has been incorporated into the till sequence. Hence, ¹⁰Be inventories in the tills are dominated by material recycled from Middle Pleistocene or older soils, near-surface sediments and saprolite, and cannot be used to date the periods of till deposition. The retention of relict ¹⁰Be in the tills nonetheless confirms minimal glacial erosion.Concentrations of meteoric ¹⁰Be in the saprolites are lower than any reported saprolite concentrations measured in other settings. Uncertainty in the pre-glaciation ¹⁰Be concentrations in the saprolites makes age determinations difficult. One possibility is that that the saprolite had higher ¹⁰Be concentrations in the past but that saprolite formation ended after glaciation and burial by till and that the ¹⁰Be has substantially decayed. Modelling of the meteoric ¹⁰Be depth profiles in this case suggests that the saprolites in the Parkajoki area were formed at a minimum of 2 Ma. Erosion of the saprolite allows an older age of up to ∼5 Ma, with up to 250 cm of material removed and incorporated into later tills. A second possibility is that concentrations of meteoric ¹⁰Be in the saprolite were originally lower, with formation of the saprolite in a period or periods of ice- and permafrost-free conditions before 0.8 Ma.     

An in situ 14C–10Be Bayesian isochron approach for interpreting complex glacial histories

We present a Bayesian isochron approach to interpret measurements of multiple cosmogenic nuclides from glacially modified bedrock surfaces with complex exposure histories. An isochron approach explicitly incorporating glacial erosion is ideally suited for this problem; such erosion must be accounted for but has traditionally been ignored. Previous methods required treating each sample individually (to account for glacial erosion) and subsequently averaging results for the entire dataset. Geological considerations, however, suggest a more robust approach is to treat samples in the dataset here (and samples from other conceivable datasets) simultaneously. The Bayesian isochron method is applied to a previously published set of in situ ¹⁴C and ¹⁰Be measurements from a set of samples spanning the forefield of the Rhone Glacier, Switzerland. Results indicate 6.4 ± 0.5 kyr of integrated exposure and 4.7 ± 0.5 kyr of cumulative burial, similar to previous estimates, but with much smaller uncertainties. The reduced uncertainties result from fitting the exposure and burial duration to the entire dataset, while explicitly accounting for glacial erosion. The method presented here should be applicable with minor modifications in a number of geologic settings, and further demonstrates the utility of paired in situ ¹⁰Be and ¹⁴C measurements for unraveling complex exposure histories over during the Holocene and late Pleistocene.     

40Ar/39Ar dating of the SP and Bar Ten lava flows AZ,USA: Laying the foundation for the SPICE cosmogenic nuclide production-rate calibration project

Precise ⁴⁰Ar/³⁹Ar age determinations made on basalt groundmass collected from the SP and upper and lower Bar Ten lava flows in the San Francisco and Uinkaret volcanic fields of Arizona, USA, yield ages of 72 ± 4, 97 ± 10, and 123 ± 12 ka (2σ; relative to Renne et al., 2010, 2011, full external precision), respectively. Previous ages of the SP lava flow include a K–Ar age of 70 ± 8 ka and OSL ages of 5.5–6 ka. ⁴⁰Ar/³⁹Ar age constraints, relative to the optimization model of Renne et al. (2010, 2011), of 81 ± 50 and 118 ± 64 ka (2σ; full external precision) were previously reported for the upper and lower Bar Ten lava flows, respectively. The new ⁴⁰Ar/³⁹Ar ages are within uncertainty of previous age constraints, and are more robust, accurate, and precise. Preliminary cosmogenic ³He and ²¹Ne production rates from the Bar Ten flows reported by Fenton et al. (2009) are updated here, to account for the improved quality of the ⁴⁰Ar/³⁹Ar data. The new ⁴⁰Ar/³⁹Ar age for the SP flow yields cosmogenic ³He and ²¹Ne production rates for pyroxene (119 ± 8 and 26.8 ± 1.9 at/g/yr; error-weighted mean, 2σ uncertainty; Dunai (2000) scaling method) that are consistent with production rate values reported throughout the literature. The ⁴⁰Ar/³⁹Ar and cosmogenic ³He and ²¹Ne data support field observations indicating the SP flow has undergone negligible erosion. The SP flow contains co-existing phenocrysts of olivine and pyroxene, as well as xenocrysts of quartz in a fine-grained groundmass facilitating cross-calibration of cosmogenic production rates and production-rate (³He, ¹⁰Be, ¹⁴C, ²¹Ne, ²⁶Al, and ³⁶Cl). Thus, we propose the SP flow is an excellent location for a cosmogenic nuclide production-rate calibration site (SPICE: the SP Flow Production-Rate Inter-Calibration Site for Cosmogenic-Nuclide Evaluations).     

Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.     

Surface exposure dating of Holocene basalt flows and cinder cones in the Kula volcanic field (Western Turkey) using cosmogenic 3He and 10Be

The Kula volcanic field in Western Turkey comprises about 80 cinder cones and associated basaltic lava flows of Quaternary age. Based on geomorphological criteria and K-Ar dating, three eruption phases, β2–β4, were distinguished in previous studies. Human footprints in ash deposits document that the early inhabitants of Anatolia were affected by the volcanic eruptions, but the age of the footprints has been poorly constrained. Here we use ³He and ¹⁰Be exposure dating of olivine phenocrysts and quartz-bearing xenoliths to determine the age of the youngest lava flows and cinder cones. In the western part of the volcanic field, two basalt samples from a 15-km-long block lava flow yielded ³He ages of 1.5 ± 0.3 ka and 2.5 ± 0.4 ka, respectively, with the latter being in good agreement with a ¹⁰Be age of 2.4 ± 0.3 ka for an augen gneiss xenolith from the same flow. A few kilometers farther north, a metasedimentary xenolith from the top of the cinder cone Çakallar Tepe gave a ¹⁰Be age of 11.2 ± 1.1 ka, which dates the last eruption of this cone and also the human footprints in the related ash deposits. In the center of the volcanic field, a basalt sample and a metasedimentary xenolith from another cinder cone gave consistent ³He and ¹⁰Be ages of 2.6 ± 0.4 ka and 2.6 ± 0.3 ka, respectively. Two β4 lava flows in the central and eastern part of the volcanic province yielded ³He ages of 3.3 ± 0.4 ka and 0.9 ± 0.2 ka, respectively. Finally, a relatively well-preserved β3 flow gave a ³He age of ∼13 ka. Taken together, our results demonstrate that the penultimate eruption phase β3 in the Kula volcanic field continued until ∼11 ka, whereas the youngest phase β4 started less than four thousand years ago and may continue in the future.     

Laser-ablation ICP-MS zircon U-Pb ages for key Pliocene-Pleistocene tephra beds in unglaciated Yukon and Alaska

Tephrochronology is one of the most effective ways to correlate and date Quaternary deposits across large distances. However, it can be challenging to obtain direct ages on tephra beds when they are beyond the limit of radiocarbon dating, do not contain mineral phases suitable for ⁴⁰K-⁴⁰Ar (or ⁴⁰Ar/³⁹Ar) dating, or suitable glass shards for fission-track dating are not available. Zircon U-Pb dating by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging technique for dating young (<1 Ma) tephra. Here, we demonstrate that LA-ICP-MS zircon U-Pb dating can produce reliable ages for key tephra beds found in Yukon and Alaska. We assessed five different techniques for calculating tephra maximum depositional ages from zircon U-Pb ages for eight tephra beds. Our preferred zircon U-Pb ages (reported with 2σ uncertainties), based on a Bayesian model for calculating maximum depositional ages, are broadly consistent with previously established chronology constructed from stratigraphy, paleomagnetism, and/or glass fission track and ⁴⁰Ar/³⁹Ar ages: Biederman tephra (178 ± 17 ka), HP tephra (680 ± 47 ka), Gold Run tephra (688 ± 44 ka), Flat Creek tephra (708 ± 43 ka), PA tephra (1.92 ± 0.06 Ma), Quartz Creek tephra (2.62 ± 0.08 Ma), Lost Chicken tephra (3.14 ± 0.07 Ma), and GI tephra (542 ± 64 ka). We also present newly revised glass fission-track and ⁴⁰Ar/³⁹Ar ages recalculated from previous determinations using updated ages for the Moldavite tektite and Fish Canyon Tuff standards, and updated K decay constants. For Pleistocene age zircon crystals, corrections for ²³⁰Th disequilibrium and common-Pb are significant and must be treated with caution. Similarly, apparent tephra ages are sensitive to the choice of method used to calculate a maximum depositional age from the assemblage of individual crystallization ages. This study demonstrates that LA-ICP-MS zircon U-Pb dating can be successfully applied to numerous Pliocene-Pleistocene Alaskan-Yukon tephra, providing confidence in applying this method to other stratigraphically important tephra in the region.